1. Field of the Invention
The present invention relates to an inkjet recording apparatus that performs recording by discharging ink from a head unit mounted on a reciprocating carriage onto a recording medium.
2. Description of the Related Art
Recording apparatuses having the function of a printer, a copying machine, a facsimile machine, or the like, recording apparatuses serving as output apparatuses in a multifunction apparatus, or a work station including a computer or a word processor are designed to record images on a recording medium, such as paper or a plastic sheet, according to image information. Recording apparatuses are classified into, for example, an inkjet type, a wire dot type, a thermal transfer type, a thermosensitive type, and a laser type according to the recording method. The recording apparatuses are also classified into a serial type and a line type according to the scanning method. In a serial type recording apparatus, an image is recorded by combining main scanning for moving a recording head along a recording medium and sub-scanning for conveying the recording medium. In a line type recording apparatus, an image is recorded by performing only sub-scanning for conveying a recording medium while each line is recorded with a recording head extending in the width direction of the recording medium.
In an inkjet recording apparatus, an image is recorded by selectively discharging ink from a plurality of discharging ports provided in a recording head according to image information. For this reason, the ink in the discharging ports sometimes dries, thickens, and fixes with time, and this causes discharging failure. Further, recording quality is sometimes reduced by discharging failure resulting from paper dust or bubbles mixed in the ink in the discharging ports. Accordingly, it is common to cap the discharging ports of the recording head for protection and prevention of drying when recording is not performed. Further, in order to remove fixing ink and bubbles which may cause discharging failure, suction recovery is performed to forcibly discharge the ink containing fixing ink and bubbles by applying a negative suction force to the discharging ports by means of a pump. Recovery is also performed by preliminary discharging for discharging ink from the discharging ports, not for the purpose of recording. Further, wiping is performed to wipe off ink and dust adhering to the surroundings of the discharging ports.
In a serial type inkjet recording apparatus, a recovery mechanism for performing the above-described recovery operations is provided within a moving range of a carriage on which a recording head is mounted, and outside a recording region. One such recovery mechanism is a slide cap type cleaning mechanism which utilizes the entry of the carriage in the mechanism so that a slider holding a cap follows the carriage along a cam face. In this slide cap type cleaning mechanism, recovery is performed to suck the ink from the discharging ports of the recording head by producing a negative pressure in the cap after the recording head is capped.
In an inkjet recording apparatus disclosed in U.S. Pat. No. 6,390,592, a cap has an ink suction port and an air communication port. During suction, negative pressure is produced by a pump in a state in which the air communication port is closed, and ink is thereby sucked from discharging ports of a recording head. Then, when a carriage moves to a cleaning mechanism, an opening and closing valve for the air communication port is opened while the cap is still in tight contact with the recording head. This valve opening operation is performed by moving the carriage so that a lever of the valve provided at the bottom of the cap moves away from the cap. This releases the negative pressure in the cap. Subsequently, a discharging face of the recording head is wiped during the movement of the carriage toward the recording region.
In an inkjet recording apparatus disclosed in U.S. Pat. No. 6,913,340, a cap has only an ink suction port. During suction, a carriage moves to a position such that a recording head is brought into tight contact with the cap, and a negative pressure is produced by a pump so as to suck ink from the recording head. After suction, when the carriage further moves to the inner side of a cleaning mechanism, a cam portion provided in a cap holder comes into contact with a cam pressing portion of a base, and the cap is opened at one end. In this state, the negative pressure is released from the cap. When the pump is further driven, waste ink in the cap can be discharged.
However, since ink is separately sucked from a plurality of recording heads in U.S. Pat. No. 6,390,592, the pump serving as a negative-pressure producing unit needs to be driven forward and in reverse. For this reason, there are many operational and structural limitations in reducing the number of motors. Moreover, an additional mechanism is necessary to release the negative pressure in the cap. This also increases the number of components.
In U.S. Pat. No. 6,913,340, when suction recovery is performed for a plurality of recording heads, ink cannot be sucked from the recording heads on an individual basis. Therefore, it is impossible to perform suction recovery only for one or some of the recording heads. As one of the measures thereagainst, it is conceivable to provide a plurality of caps corresponding to the recording heads, and to individually suck ink from the recording heads by means of cams provided in only one, some, or all cap holders. However, in this case, if capping is performed while the pump is closed before ink is sucked from the recording head, a small positive pressure is applied to the discharging ports of the recording head. The positive pressure pushes ink disposed near the discharging ports into ink chambers. Therefore, preliminary discharging or suction recovery is inevitable in order to obtain high recording quality.
It is also conceivable to perform suction after the recording head is capped with the pump open. However, in this control method, the operating position of the pump, for example, the position of a pressing roller in the tube pump, varies, and this causes variations in the amount of ink sucked in sucking operations.